Cathode grid assembly



Sept. 23, 1952 E, PQHLE 2,611,676

CATHODE GRID ASSEMBLY Original Filed May 13, 1950 2 SHEETS-SHEET 1 INVENTOR. ERIC POHL E ATTORNEYS Patented Sept. 23, 1952 T' '1 2,611,676 CATHODE GRID ASSEMBLY Eric Pohle, Clifton, N. J., assignor to Allen B. Du Mont Laboratories, Inc., Clifton, N. J., a corporation of Delaware Original application May 13, 1950, Serial No.

161,793. Divided and this application October 20, 1951, Serial No. 252,371

. l This invention relates to electron discharge devices and particularly to the electron gun portion of cathode ray tubes, and more particularly to a method for making the cathode grid assembly of said tubes. This is a division of my application, Serial No. 161,793 filed May 13, 1950, now Patent No. 2,582,454.

In the manufacture of cathode grid assemblies for cathode ray tubes, a mechanical spacer has been used to fix the distance between the electron emissive coating onthe cathode and the grid aperture. Since the distance to be controlled is of the order of .005 inch, a tolerance of +10% requires that these spacers vary in size no more than +0005 inch. It, is dimcult to obtain pressed or drawn metal spacers having the required accuracy and a large percentage must be rejected. Furthermore, since the error is not entirely confined to the spacer but may be the result of incorrect stamping of other .elements of the structure, it frequently happens that the complete cathode grid assembly is constructed before it is found to be outside of the tolerances thereby increasing the expense of the rejected part.

Other cathode grid assemblies which have been made without the use of mechanical spacers to determine the spacing between the cathode and grid, have been subjected to a tilting of the axis. of the cathode with respect to the grid. This cannot be controlled because of the inaccessibility of the cathode and cannot be determined "until the cathode ray tube is completed and tested.

Consequently one object of my invention is to provide an improved cathode grid assembly.

A second object is to provide a cathode grid assembly, for a cathode ray tube, which can be rapidly and accurately assembled.

Other objects will be apparent from the specification and drawings in which:

Figure 1 is an isomeric view of a cathode grid assembly; 7

Figure 2 shows a bottom view of the cathode assembly in Figure 1;

Figure 3 is a cross sectional view through 33 of the device in Figure 2;

Figure 4 shows a cathode thimble in its holder;

Figure 5 is a bottom view of the device in Figure 4;

Figure 6 illustrates apparatus used in one method of assembly of a cathode grid assembly; and

Figure '7 is a bottom view of one part of the device shown in Figure 6.

'4 Claims. (01.316-23) 2 V ,5 The invention will be described with reference to Figure 3, in which a cathode ray tube grid cylinder II is shown, made in accordance'with known principles. One end of the cylinder H is capped by a disc |2 having a ring I 3 on the rim thereof clasped by the matching rib M on the cylinder The disc |2 has a central aperture l6 and a stifiening' rib H. v

The cathode comprises acap l8 on which the emitting material [9 is located and a sleeve 20 inserted in and preferably welded to the cap I8 to form the complete cathode structure. "This structure is mounted in the centrally located hole of a ceramic disc 2| and is held in place by the flange 22 of cap I8 on one side and by a bead -23 pressed into the cylinder 20 on the other side of the disc 2|.

Figures 4 and 5 show the disc 2| held in a metallic rim 24 by means of a plurality of fingers 26 which are cut from the cylindrical side of the rim 24. Theopenings 25 in the disc 2| assist in the evacuation of the cathode grid structure during the final construction of the cathode ray tube. The rim 24 has a slot 21 therein for a purpose to be hereinafter explained.

Figure 6 shows a cathode grid similar to th one in Figure 3 in position for sealing the rim -24 to the grid cylinder The reference characters III and 2 indicate that the parts so designated are electrically equivalent to parts designated II and I2 in Figure 3. They difier mechanically in that the cylinder Hi and the may be part of a vise 28, moved vertically by means of a knob 32, may be used to locate ac curately the cathode with respectto' the anode. In assembling the cathode grid structure, the vise 28 is opened as shown in Figure 7, which is a bottom view, and the cylinder III is slipped in place. The cylinder III is locked in place with the disc 2 against the shoulder 33 of the vise 28. Space 34 is provided for the rim I4 if a structure such as that shown in Figure 3 is used.

If a one piece grid cylinder Ill and disc 2 is used, the focus of the microscope 3| can be fixed on a point which is below the top surfaceoi. the disc 2 by a distance equal to the thickness of the disc H2 plus .005 inch, or the desired spacing. If a grid structure such as is shown in Figure 3 is used, the stiffening ring I! forms the abutting surface for the disc l2 against the shoulder 33.

Since the height of the rub Il may vary, it is necessary first to focus the microscope 3! on the top surface of the disc i2 adjacent the aperture i6 and then refocus on a second point the required distance below the first point. Any of a number of well known gauging techniques may be used to determine the relation between the first and second focussing points.

Having fixed the microscope 3| at the second focussing point, the cathode assembly is then inserted into the grid cylinder III. A mounting device 29, mounted on guides (not shown) which allow it to slide coaxially into the cylinder Ill, may be used to insert the cathode assembly into the position where the emissive material 19 is at the second focussing point. The device'29 has a central pole 34, which fits snugly into the cathode cylinder 20 to keep it from tilting with respect to the grid cylinder 1 I l, and arms 36, which may be in the form of an open ended cylinder. The arms 36 form the abutting surfaces since they rest on the comparatively sturdy insulating disc 21,, while the central pole serves as the guide.

When :the cathode assembly is properly positioned within the grid cylinder Hi, the welding electrodes '31 and 38 spot weld the'rim 24' to the cylinder Hi to complete the construction of the cathode grid-assembly.

The .purposeof the slot-21 .in the rim 24 (Figs. 4: and is to allow the rim 24- to be made with aslightly larger external diameter than the internal diameter of the cylinder Hi. This results insome friction, which is desirable, when the-cathode assembly is inserted in the cylinder Hi. This friction, if not excessive, aids in positioning the cathode assembly properly within the cylinder ill by resisting relative movement between the rim 24 and the cylinder H l, thus holding the disc 2! tightly against the arms 36.

inner diameter of the skirt portion of the rim 24.

The fingers 26, instead of the ceramic 2|, will then rest on top of the arms 36, but since the center aligning. rod 34 maintains the alignment of the cathode, the assembly will not be misaligned.

A third way of welding. the rim to the cylinder i l I isto utilize only the welding electrodes 37 in which case the mounting device '29 need not even be constructed'of conducting material. This last mentioned type of welding consists in-applying one polarity of the welding potential to one of the electrodes 31 and the other polarity to the other electrode 31. Welding then takes place at the areas of contact of the rim 24 and the cylinder i ll closest to the two electrodes 31.

Although I have illustrated this invention by specific examples of cathode grid assemblies and manufacturing devices, obvious alternatives will occur to those skilledin the art, and therefore I 'do not desire to be limited except by thefollow- Zingclaims.

What is claimed is:

1. The method of making a cathode grid as sembly for a cathode ray tube which consists in forming a grid in the form of a cylinder closed at one end with an aperture centrally located in said closed end, forming a cathode in the form of a cylinder closed at one end, coating the outer surface of the closed end of said cathode, inserting said cathode coaxially within said grid with the respective closed ends in the same longitudinal direction, optically focussing on the closed end of said grid, thereafter optically focussing on a'point in space through said aperture at a predetermined desired distance therefrom, and longitudinally positioning said cathode on said point insp'ace.

2. The method of making a cathode-grid assembly for a cathode ray tube which comprises the-steps of forming a first cylinder having a closed end, forming a second cylinder having a. closed end, positioning said cylinders with their closed ends in juxtaposition, Ffocussing ia llens system of predetermined focal length on the closed end of said first cylinder, moving saidsystem a predetermined-distance with respect'to said first cylinder, positioning said second cylin'der'so that said system is focuss'ed on the closed end thereof and thereafter securing. said. cylinders together.

3. The method of making a .cathode-grid =assembly for a cathode ray. tube which comprises the steps of forming afirst cylinder hav-ing a closed end with an aperture therein, :formi'ng a second cylinder 'withba closed-end, 'providinga coating of electron emissive material--onsaid closed 'endof said second cylinder, coaxially' positioning said cylinders, said second mentioned cylinder being within said first mentioned cylinder with said coating in juxtaposition with the closed end-of said firstcylinder focu'ssing a lens system of predetermined focal -length on the closedend of said first cylinder, moving'said 'system a predetermined distanc'ealon'g the longitudinal axis .of said cylinders, positioning said second cylinder so that system is focussed on said coating and thereafter securing said-cylinders together.

4. The method of :making cathode gri'd as sembly for a cathode ray tube which comprises the steps of forming .a first cylinder-having :a

closed end with an aperture therein, forming-La second cylinder with a closed end, saidlzsecon'd cylinder being of smaller diameter thansaidffirst cylinder, providing a coating of electron-:emissive material on the external surface on thei-iclosed end of said second.cylinder,;,coaxially positioning said cylinders with said coating in juxtaposition with the apertureat the closed end of said first cylinder, positioning a 'lens'system of predeterminedfocal length so that the focal axis :of' said 

